1. Technical Field
The present invention relates to information systems technology. More particularly, the present invention relates to the storage of information in a computer system. Still more particularly, the present invention relates to a method and system of merging physical groups of storage devices.
2. Description of Related Art
The UNIX operating system, or xe2x80x9cUNIX,xe2x80x9d xe2x80x9cA weak pun on Multics,xe2x80x9d is an interactive time-sharing operating system invented in 1969 by Ken Thompson after he left Bell Labs and the Multics project, apparently to play games on his scavenged PDP-7 computer (minicomputer sold by Digital Electric Corp. (DEC), (Compaq Computer Corp., 20555 SH 249, Houston, Tex. 77070)). Thompson developed a new programming language xe2x80x98Bxe2x80x99, and Dennis Ritchie enhanced xe2x80x98Bxe2x80x99 to xe2x80x98Cxe2x80x99 and helped develop xe2x80x98UNIXxe2x80x99.
The UNIX operating system is a multi-user operating system supporting serial or network connected terminals for more than one user. It supports multi-tasking and a hierarchical directory structure for the organization and maintenance of files. UNIX is portable, requiring only the kernel ( less than 10%) written in assembler, and supports a wide range of support tools including development, debuggers, and compilers.
The UNIX operating system consists of the kernel, shell, and utilities. The kernel schedules tasks, manages data/file access and storage, enforces security mechanisms, and performs all hardware access. The shell presents each user with a prompt, interprets commands typed by a user, executes user commands, and supports a custom environment for each user. Finally, the utilities provide file management (rm, cat, ls, rmdir, mkdir), user management (passwd, chmod, chgrp), process management (kill, ps), and printing (lp, troff, pr).
A multi-user operating system allows more than one user to share the same computer system at the same time. It does this by time-slicing the computer processor at regular intervals between the various people using the system. Each user gets a set percentage of some amount of time for instruction execution during the time each user has the processor. After a user""s allotted time has expired, the operations system intervenes, saving the program""s state (program code and data), and then starts running the next user""s program (for the user""s set percentage of time). This process continues until, eventually, the first user has the processor again.
It takes time to save/restore the program""s state and switch from one program to another (called dispatching). This action is performed by the kernel and must execute quickly, because it is important to spend the majority of time running user programs, not switching between them. The amount of time that is spent in the system state (i.e., running the kernel and performing tasks like switching between user programs) is called the system overhead and should typically be less than 10%.
Switching between user programs in main memory is done by part of the kernel. Main system memory is divided into portions for the operating system and user programs. Kernel space is kept separate from user programs. Where there is insufficient main memory to run a program, some other program residing in main memory must be written out to a disk unit to create some free memory space. A decision is made about which program is the best candidate to swap out to disk. This process is called swapping. When the system becomes overloaded (i.e., where there are more people than the system can handle), the operating system spends most of its time shuttling programs between main memory and the disk unit, and response time degrades.
In UNIX operating systems, each user is presented with a shell. This is a program that displays the user prompt, handles user input, and displays output on the terminal. The shell program provides a mechanism for customizing each user""s setup requirements, and storing this information for re-use (in a file called profile).
When the UNIX operating system starts up, it also starts a system process (getty) which monitors the state of each terminal input line. When getty detects that a user has turned on a terminal, it presents the logon prompt; and once the password is validated, the UNIX system associates the shell program (such as sh) with that terminal (typically there are a number of different shells including ksh and csh). Each user interacts with sh, which interprets each command typed. Internal commands are handled within the shell (set, unset);
external commands are invoked as programs (ls, grep, sort, ps).
Multi-tasking operating systems permit more than one program to run at once. This is done in the same way as a multi-user system, by rapidly switching the processor between the various programs. OS/2, available from IBM Corporation, One New Orchard Road, Armonk, N.Y. 10504; and Windows 95, available from Microsoft Corporation, One Microsoft Way, Redmond, Wash. 98052, are examples of multi-tasking single-user operating systems. UNIX is an example of a multi-tasking multi-user operating system. A multi-user system is also a multi-tasking system. This means that a user can run more than one program at once, using key selections to switch between them. Multi-tasking systems support foreground and background tasks. A foreground task is one the user interacts directly with using the keyboard and screen. A background task is one that runs in the background (i.e., It does not have access to the screen or keyboard.). Background tasks include operations like printing, which can be spooled for later execution.
The role of the operating system is to keep track of all the programs, allocating resources like disks, memory, and printer queues as required. To do this, it must ensure that one program does not get more than its fair share of the computer resources. The operating system does this by two methods: scheduling priority, and system semaphores. Each program is assigned a priority level. Higher priority tasks (like reading and writing to the disk) are performed more regularly. User programs may have their priority adjusted dynamically, upwards or downwards, depending upon their activity and available system resources. System semaphores are used by the operating system to control system resources. A program can be assigned a resource by getting a semaphore (via a system call to the operating system). When the resource is no longer needed, the semaphore is returned to the operating system, which can then allocate it to another program.
Disk drives and printers are serial in nature. This means that only one request can be performed at any one time. In order for more than one user to use these resources at once, the operating system manages them via queues. Each serial device is associated with a queue. When a user program wants access to the disk, for example, it sends the request to the queue associated with the disk. The operating system runs background tasks (called daemons), which monitor these queues and service requests from them. A request is then performed by this daemon process, and the results are sent back to the user""s program.
Multi-tasking systems provide a set of utilities for managing processes. In UNIX, these are ps (list processes), kill (kill a process), and and (run a process in the background). In UNIX, all user programs and application software use the system call interface to access system resources like disks, printers, memory etc. The system call interface in UNIX provides a set of system calls (C functions). The purpose of the system call interface is to provide system integrity. As all low level hardware access is under control of the operating system, this prevents a program from corrupting the system.
The operating system, upon receiving a system call, validates its authenticity or permission, then executes it on behalf of the program, after which it returns the results. If the request is invalid or not authenticated, then the operating system does not perform the request but simply returns an error code to the program. The system call is accessible as a set of xe2x80x98Cxe2x80x99 functions, as the majority of UNIX is also written in xe2x80x98Cxe2x80x99. Typical system calls are: _readxe2x80x94for reading from the disk unit; _writexe2x80x94for writing to the disk unit; _getchxe2x80x94for reading a character from a terminal; _putchxe2x80x94for writing a character to the terminal; and _ioctlxe2x80x94for controlling and setting device parameters.
The fundamental structure that the UNIX operating system uses to store information is the file. A file is a sequence of bytes, typically 8 bits long, and is equivalent to a character. UNIX keeps track of files internally by assigning each one a unique identifying number. These numbers, called inode numbers, are used only within the UNIX operating system kernel itself. While UNIX uses inode number to refer to files, it allows users to identify each file by a user-assigned name. A file name can be any sequence containing from one to fourteen characters.
There are three types of files in the UNIX file system: (1) ordinary files, which may be executable programs, text, or other types of data used as input or produced as output from some operation; (2) directory files, which contain lists of files; and (3) special files, which provide a standard method of accessing I/O devices.
UNIX provides users with a way of organizing files. Files may be grouped into directories. Internally, a directory is a file that contains the names of ordinary files and other directories, and their corresponding inode numbers. Given the name of a file, UNIX looks in the file""s directory and obtains the corresponding inode number for the file. With this inode number, UNIX can examine other internal tables to determine where the file is stored and make it accessible to the user. UNIX directories themselves have names, each of which may also contain fourteen characters.
Just as directories provide a means for users to group files, UNIX supports the grouping of directories into a hierarchical file system. At the very top of a hierarchy is a directory. It may contain the names of individual files and the names of other directories. These, in turn, may contain the names of individual files and still other directories, and so on. A hierarchy of files is the result. The UNIX file hierarchy resembles an upside-down tree, with its root at the top. The various directories branch out until they finally trace a path to the individual files, which correspond to the tree""s leaves. The UNIX file system is described as xe2x80x9ctree-structured,xe2x80x9d with a single directory. All the files that can be reached by tracing a path down through the directory hierarchy from the root directory constitute the file system.
UNIX maintains a great deal of information about the files that it manages. For each file, the file system keeps track of the file""s size, location, ownership, security, type, creation time, modification time, and access time. All of this information is maintained automatically by the file system as the files are created and used. UNIX file systems reside on mass storage devices such as disk files. These disk files may use fixed or removable type media, which may be rigid or flexible. UNIX organizes a disk as a sequence of blocks, which compose the file system. These blocks are usually either 512 or 2048 bytes long. The contents of a file are stored in one or more blocks, which may be widely scattered on the disk.
An ordinary file is addressed through the inode structure. Each inode is addressed by an index contained in an i-list. The i-list is generated based on the size of the file system, with larger file systems generally implying more files and, thus, larger i-lists. Each inode contains thirteen 4-byte disk address elements. The direct inode can contain up to ten block addresses. If the file is larger than this, then the eleventh address points to the first level indirect block. Address 12 and address 13 are used for second level and third level indirect blocks, respectively, with the indirect addressing chain before the first data block growing by one level as each new address slot in the direct inode is required.
All input and output (I/O) is done by reading the writing files, because all peripheral devices, even terminals, are files in the file system. In a most general case, before reading and writing a file, it is necessary to inform the system of your intent to do so by opening the file. In order to write to a file, it may also be necessary to create it. When a file is opened or created (by way of the xe2x80x98openxe2x80x99 or xe2x80x98createxe2x80x99 system calls), the system checks for the right to do so and, if all is well, returns a non-negative integer called a file descriptor. Whenever I/O is to be done on this file, the file descriptor is used, instead of the name, to identify the file. This open file descriptor has associated with it a file table entry kept in the xe2x80x9cprocessxe2x80x9d space of the user who has opened the file. In UNIX terminology, the term xe2x80x9cprocessxe2x80x9d is used interchangeably with a program that is being executed. The file table entry contains information about an open file, including an inode pointer for the file and the file pointer for the file, which defines the current position to be read or written in the file. All information about an open file is maintained by the system.
In conventional UNIX systems, all input and output is done by two system calls, xe2x80x98readxe2x80x99 and xe2x80x98write,xe2x80x99 which are accessed from programs having functions of the same name. For both system calls, the first argument is a file descriptor. The second argument is a pointer to a buffer that serves as the data source or destination. The third argument is the number of bytes to be transferred. Each xe2x80x98readxe2x80x99 or xe2x80x98writexe2x80x99 system call counts the number of bytes transferred. On reading, the number of bytes returned may be less than the number requested, because fewer than the number requested remain to be read. A return value of zero implies end of file, a return value of xe2x88x921 indicates an error of some sort. For writing, the value returned is the number of bytes actually written. An error has occurred if this is not equal to the number which was supposed to be written.
The parameters of the xe2x80x98readxe2x80x99 and xe2x80x98writexe2x80x99 system calls may be manipulated by the application program that is accessing the file. The application must, therefore, be sensitive to and take advantage of the multi-level store characteristics inherent in a standard system memory hierarchy. It is advantageous, from the application perspective, if the system memory components can be viewed as a single level hierarchy. If this is properly done, the application could dispense with most of the I/O overhead.
One advantage of using a UNIX based operating system over another operating system is that data can be isolated or segregated into different volume groups (VGs). The omnipresent xe2x80x9crootvgxe2x80x9d contains the operating system details, and it is from this volume group that the computer runs. Similarly, data or application volume groups can also be created. The advantage of such volume groups is that, unlike competitive operating systems, an upgrade to a UNIX based operating system will only impact the rootvg, and will not affect application data. Analogously, application upgrades will not impact the operating system in any way, presuming that the application has been segregated into its own VG.
In today""s dynamic information systems (IS) environment, organizational components experience constant change. These changes involve everything from operating system and application upgrades, to network infrastructure, to data layouts across disks. This last concept, the movement of data into new storage locations, has become increasingly prevalent given the ever more complex disk configurations that IS shops are using. In the days when disk sizes were measured in megabytes, and arrays were nonexistent, data architectures remained relatively static. In today""s large IS shops, however, where SSA or SCSI disk arrays provide storage in the tens or hundreds of gigabytes, the physical layout of data upon those disks often has a need to change.
An example of this would be a database whose needs have grown faster than expected, and a customer with a requirement to move data from a simple mirror configuration into a larger volume group. Previously, any such data rearrangement, complex though it might have been, had to be executed manually. Manual execution of such changes has been the norm. Moreover, the data contained in the database must itself be copied to an external storage system and verified before the filesystems and volume group can be removed in favor of an expanded volume group. Only then can the physical disks be included into the new volume group and the filesystems and files recreated in the new volume group.
It would be advantageous to provide rapid and reproducible solutions in the UNIX environment. It would further be advantageous to provide a script for allowing quicker, more comprehensive rearrangement and combination of UNIX data structures. It would be even more advantageous to provide an automated tool for performing these processes, so that the processes can be accomplished more quickly and more efficiently, with less room for administrator error.
The present invention relates to a system and method for merging volume groups on a UNIX based computer system. Initially, a filesystem map is created, and the logical control volume block is copied outside the volume group. The initial logical volume is deleted, and the disks are removed from the definition of the old volume group. The definition of the new volume group is defined to include the disks formerly defined in the old volume group. The filesystem map that was created is used to recreate the filesystem in the new volume group, and the volume control block is copied into the new volume group. The filesystems are reinstated onto the new volume group and remounted.